After jets crashed into the World Trade Center, the Pentagon, and the Pennsylvania woods, a stand-up comedian I know stopped performing. In the face of such an enormity, he wondered, how could we ever laugh again? The aftermath of 9/11, particularly in New York City, was a surreal world of death and wreckage, an alternate reality from which there seemed no escape. Yet it’s natural — indeed, a profound human need — to want to forget, to want to get back to the routine of everyday life: work, school, kids, sports, and the myriad other activities that regularly fill our days. And so eventually (and quite soon in fact) we did.

Almost 12 years later, we are seeing that same impulse in Boston. The Back Bay portion of Boylston Street is the city’s main street, a 1½-mile stretch running from the Common to the Fenway. It is not only the finish line of the Marathon, but an extraordinary mix of colleges, churches, offices, hotels, the Boston Public Library, Copley Square, and all kinds of restaurants, bars, and retailers packed shoulder-to-shoulder. It’s the chic and the hick (a play on words that works better if not read aloud): L’Espalier, Marshalls, the Apple Store, Dunkin’ Donuts, Lord & Taylor, Supercuts, and dozens of others.

For nine days, the street was largely empty. On Wednesday, after cleaning crews had removed the blood, paint, and debris from what had been a vast crime scene, it reopened and, like a rubber band stretched and then released, people surged back in, jamming sidewalks and the roadway.

As one walked the street’s length, there was little left to mark the horrors of that Monday. Marathon Sports, across from the library, was the site of the first blast. A small crowd gathered in front, forming a semicircle and snapping pictures. Ten or so bouquets of flowers, some with notes of condolence, others with words of hope, were laid out on the pavement in a neat line. The scene was the same at the Forum restaurant, just one block west and the location of the second blast: Crowds, semicircle, pictures, flowers. Aside from a few boarded up windows, it was as if the bombings had never happened.

The physical traces of the tragedy are nearly gone. Can memory be far behind?

For five days, the Marathon bombings gripped the nation. It wasn’t just the casualties; two days later, an explosion at a fertilizer plant in Texas killed far more. But an accident is one thing; intentional is altogether different. The images played out endlessly on televisions and computer screens. As with the jets crashing into the twin towers, we saw — from multiple cameras and multiple perspectives — the exact moment terror was unleashed. And we saw it viscerally, at ground level, as bodies lay strewn on sidewalks, blood flowing from grievous wounds.

We saw courage too, as well as resilience and healing. We saw a city come together with extraordinary unity, a city that mourned, deeply and genuinely, the lives lost. We saw drama: a manhunt and the lockdown, an episode of “Homeland’’ in our backyards. There was more death, firefights, an overwhelming show of force, seeming failure, and then, by the luckiest of chances, capture.

There remain so many questions. How could such terror be unleashed, allegedly by two loners with (it appears) little money and no backing? How could two men with such promise have become so utterly twisted? How had they been able to shed their humanity to such a degree that they could place their bags on the street, look directly into the eyes of their victims, and still trigger the blasts?

Boston has endured and survived. A year from now, we’ll undoubtedly mark the anniversary in some special and somber way. But we need something more than that, something more than video clips, more than Wikipedia entries, more than plaques placed on building walls. We need something permanent, a memorial, something physical and significant built right in the heart of the Back Bay that honors victims, recognizes those affected, tells a story, and, most importantly, helps us understand. It’s the next task before us. Even as we forget, we must make sure we’ll always remember.